Stereoscopic system



March 9, 1943 P. MAINARDI arm. STEREOSCQPIC SYSTEM:

4 Filed ma 22, 1941 2 Sheets-Sheet 1" pOMPEYMA/NARD/ MARCUS NMA/NARD/ INVENTORS A TT ORNE Y March 9, 1943. p, MAINARDI A 2,313,561

STEREOSGOPIG SYSTEM I 2 SheetsShe't 2 Filed May '22. 1941 ARM: 8

Q pOMPEYMA/NARD/ MARCUs/YMA/NARD/ I N V EN TORS Patented Mar. 9 1943 STEREOS'COPIC SYSTEM Pompey Mainai'di and Marcus mommies Paterson, N. J.

Application May 22, 1941, Serial No. 394,677

12 Claims.

This invention relates to stereoscopic sys= tems, particularly to those of the type described in my copemiing application, Serial Number 394,676 filed concurrently herewith.

In optical systems for projecting from and particularly for taking stereoscopic pictures ad iacent to one another on a film, with the images oppositiaxially oriented on the film, various double-mirror systems are possible. A preferred form or such systems as described in my copending application, involves an lscceles pris preferably an equilateral prism immediately in front of the camera or projector objective. The simplest form of such a. system, particularly when used on o. camera, requires the camera to be held at an angle. It is the primary object of the present invention, to provide moons where" by the camera may he held at a more coriyori ierit angle and still give properly oriented images.

The invention is eousliy'appiicolole to e simple mirror system, i. e., one not employing a prism. in this case and also in the case oi the prism where an additional mirror is cooled to the sys term, the cbiect of the invention is to permit the use of srnciler mirrors.

Uppositiaxiel images, i. e., images which ore lieati-to-heud or ioot-to-foot on the film and adjacent to one another, have two tid /outages, in the first place, their width is greater than their height which is desirable in the majority of pictures and iii the second plate keystone distortion is either entirely eliminated, or tithe camera is tipped at an angle to the horizontal, the iseystone distortion is identical in the two pictures and hence introduces no eyestrairi when an attempt is made to fuse the pictures stereoscopically. In addition to simplicity and accuracy, the use of a prism as described in my copending application permits the lens to he used efiicieritly for each of the pictures. The

present invention simplifies the construction of the optical systems necessary to give these acivantsges and makes the systems more-compact and more convenient to use.

facesin front of the camera or projector lens to reflect the light coming to or from the lens and two outer reflectors preferably separated at the interocular distance, to receive light from i the subject and reflect it to the intersecting refleeting surfaces, in the case of a camera and vice versa. in the case of a. projector. In order that the system be as compact and convenient as possible, the point of intersectiofi between the reflecting surfaces is tipped at an acute angle to the principal planes of the lens, preterably between 5 and 25, i. e., about 15.

Of course, sincelight may travel in either direction through an optical system comprising simple reflecting surfaces and lenses, the optical system may be described, with respect to either direction of the light beams but the same system can be used either for projecting or taking.

Since most projectors require that the projectionlamp be held in a vertical position and are made so that the lens has its optic axis whstoiitially horizontal, it is usually desirable to provide means for using the projector without changing the orientation of its lens. As pointed out in my copending application, this may be done by the use of so. additional mirror in the stereoscopic system or by rotating the whole system through 99% and placing a mesh at the screen itself. In either of these errsiisemeots, there is littleor no advantage gained inrhoyios the intersecting reflecting surfaces tipped us just described. Therefore, the present invers tion is most imeiui tor cemeros and 'Wiil. he de scribed particularly in that connection. invention is most useful when on eouilotcrcl prism is used, but with either mirrors or prisms, the angle between the litre of intersection the principal plahesoi the lens should be he I tween 5 and 25 and preierably about iii An attachment for a camera may he made up with the prism adjacent to one Window in the housing oi the attachment and so oriented hehind that window, that when the housing is st torched to the camera lens, the prism is tipped ot the desired angle. The front window of the housing through which iight'from the subject strikes" the two outer reflectors is so arranged that the top or bottom edge of the window acts as e mask to prevent light in either beam overlapping the other beam at the rear focus oi. the

lens. Since the amount of masking would, olepend on vignetting and varywith lens aperture, this mask is preferably adjustable. It is convenient to provide such anattachment with a view finder mounted centrally above the prism and oriented so that its optic axisis parallel to rays from that part-of the subject which cor= responds to the mid point of each half of the picture frame at the back focus plane of the lens.

In the case where the intersecting reflectors consist of mirrors, the angle between these mirrors may be adjusted to any convenient orientation. In this case, the angle between the line of intersection and the prinicipal planes of the lens depends on the angle between the mirrors themselves, but for the purpose of the present inven- 5 tion, it is still preferably in the range of 5 to 25". Of course, when a prism is used whose vertex angle is 60, it is not absolutely necessary that the base face of the prism be parallel to this apex. However, for convenience in manufacture, this base face should be parallel to the apex,

" Fig. 1 shows one embodiment of the invention in elevation, partly in cross section;

Fig. 2 shows a slight variation of theembodiment shown in Fig. 1.

Fig. 3 is a perspective view showing the principal elements of the invention.

Fig. 4 is a similar showing of an embodiment of the invention using mirrors instead of a prism. Fig. 5 is a perspective view of an attachment for a camera incorporating the present invention.

One-half of a stereoscopic optical system is shown in Fig. 1 and consists of a reflector ill, a reflecting surface H, a lens I2, and a back focus plane l3. The outer mirror ill and the corresponding mirror in the other half of the system are spaced apart the interocular distance or possibly some other distance if accentuated stereo effects are desired. As the light beamsare traced through the optical system in this drawing, the reflecting surface II is considered as one side face of an isosceles prism whose base face is adjacent to the lens l2 and'tipped at an angle A with respect .to the principal planes thereof. As shown by rays I4 and 15, light from the subject being photographed proceeds upright as shown by arrow 20 and strikes the mirror in as shown by the arrow 2| whence it is reflected through one of the side faces of the prism II to form. the arrow 22. None of these arrows. are actual images but merely show the orientation of the pencil of rays. face of the prism together with any refraction due to the angle of incidence, the rays strike the other side face as shown by the arrow22' and are reflected from there through the base face of the prism and through the lens 12 to the imagesplane A view finder for the system comprising a front lens I1 and an eye-piece I8, is conveniently mounted above and symmetrically between the two outer reflectors represented by the mirror in,

with the optic axis of the view finder directed toward the center of the field of view, parallel to a line bisecting the angle between the rays II and I5.

The raysfrom each half of the system cross each other in the lens l2 and are imaged oppositiaxially on the film I; as best seen in Fig. 3. A mask 38 cutting off all rays above the ray I4 is provided to prevent any portion of either beam overlapping the other beam at the image frame 83. Referring to Fig. 3, it .will be noted thateach of the beams represented by the arrows 20 are rotated in opposite directions through 90 so that the images 35 onthe image plane I! are This is best seen in Fig. 1.

After transmission through the side 50 If the apex-of the prism II were parallel to the I principal planes of the lens l2, the angle B between the focal plane J3 and the horizontal (corresponding to the rays I4) is quite large and the camera extends back so that it is not convenient for the operator to place his eye I! immediately behind the ocular I! of the eye-piece. For many 5 purposes it is desirable to hold the camera as nearly upright as possible during the taking of pictures. By means of a holder 23, the apex of the prism I l is held at an acute angle A to the principal planes of the lens i2. In the arrange ment shown in Fig. 1 the base face of the prism H is parallel to the apex thereof and hence the angle A is the angle between this base face and the principal planes of the lens i2. Due to refraction and changes in the angles of reflection by the tipping of the prism to the angle A, the angle B is considerably reduced and much more convenient arrangement results.

The arrangement of the arrows 2i, 22, 22' and 22" is best seen from Fig. 3 and is best described with reference to rays traveling from the image 35 outward. The equilateral prism il acts optically as a block of glass. The rays diverging from the centre of the lens i2 striking the base face of the prism II as shown by arrow 22" continue their divergence to form the arrow 22. If this prism is drawn out as a block of glass, as is often done in optical design work, it will be noticed that the arrow 22' lies diagonally across the diverging beam and hence it is much longer than either of the other arrows. Because of the angle A, all rays at the arrow 22 are bent downward but those traveling through the foot of the arrow do not travel as great a distance before striking the side face of the prism. Hence, the point of 5 the arrow in 22' is deviated more from the optic axis of the lens i2 than is the base of this arrow. After reflection at this surface, however, the rays traveling to the base of the arrow 22 travel much further than those to the point thereof. Hence, the arrow 22 is tipped still further as shown. The outer mirrors ii are oriented so as to provide the 90- degree rotation required.

Fig. 2 illustrates a variation of this embodiment of the invention wherein an additional mirror 22 is provided between the prism i0 and the outer mirrors 2! in this case. Due to lateral inversion, the lower ray 21 is the one corresponding to the optic axis of the lens and hence the mask 3! is placed adjacent to this ray. If the cameras shown in Figs. 1 and 2 are held as illustrated, i. e. with the rays corresponding to the optic axis of the lens, coming from the subject into the outer reflectors horizontally, there will be no keystone distortion in either of the stereo pictures. Tipping of the apparatus in either case, results in identical distortion in both pictures which is not objectionable. In Fig. 2 the upper ray from the subject represented by arrow 2! is labeled 26 and the optic axis of the viewfinder 2. is, as before,

directed toward the center of the field of view.

The images 30 andWi correspond to 2| and 22' Since the mirror 22 may be placed of Fig. 1. at various angles, it is quite possible to have the head-to-head, i. e., oppositiaxially oriented. T0 film plane it perfectly vertical. Therefore, the

' position32.

sole advantage in having the prism ll tipped at an angle A to the principal planes of the lens I2 is to permit the use of a smaller mirror in the Fig. 4 is similar to Fig. 3 and illustrates how the invention may be applied to systems using mirrors entirely; Such systems have the disadvantage of reducing the effective aperture of the lens I2 to less than half unless the line of intersection is placed a great distance in front of the lens. .However, when mirrors are used, there is considerable freedom regarding the angle C between the mirrors 31. The angle D between the 3 line of intersection thereof and the principal planes of the lens i2 depends somewhat on what angle C is chosen. If the angle C is 90 so that the rays 36 coming into the mirrors III are reflected substantially horizontally inward to the mirrors 31, angle D may be zero as is known or very small. However, for smaller values of the angle C which are preferable, it is desirable to allow the angle D to have, a finite value somewhere in the same range as for the prism, namel preferably between 5 and 25.,

The preferred embodiment of the invention is in a camera attachment as shown in Fig. 5 in which the view finder 40, having lenses l1 and- I8 corresponding to Fig. 1 is mounted on top of a housing 4| which includes the mirrors Wand prism ll of Fig. 1 and which has the front window of the housing arranged so that the upper edge of this window corresponds to the mask 38. This edge should preferably be vertically adjust which the two intersecting reflecting surfaces are the side faces of an equilateral prism whose apex is the line of intersection and whose base face is adjacent to the lens, whereby the beams between the surfaces and said two reflectors respectively pass through the opposite reflecting surface.

4. An optical system according to claim 1 in which said acute angle is about 5. An optical system for taking stereoscopic pictures adjacent to one another and oppositiaxially oriented on a film which system comprises a, camera.having an objective lens, an isosceles prism mounted in front of the lens with its base face at an appreciable acute angle between 5 and 25 to the principal planes of the lens and two reflectors on opposite sides of the prism oriented to receive light beams from the subject to be photographed, to rotate them oppositely through 90 and to reflect them respectively through the side faces of the prism to the opposite side faces which are oriented to reflect these beams through the base face and crossing] through the lens. I

6. An optical system according to claim 5 in which a mask is mounted in front of'the reflectors to cut oiffrom .each beam any portion which would overlap the other beam at the back focusplane of the lens in the camera.

able to correspond to different lens apertures.

The attachment is attached by a sleeve 42 to the lens mount 43 of a camera 44.

Having thus described the preferred embodiments of our invention, we wish topoint out that .it is not to be limited to the structures, but is of the scope of the appended claims.

What we claim and desire. to secure by Letters Patent of th United States is: 1. An optical system for projecting from or taking stereoscopic pictures adjacent to one another and oppositiaxially oriented on a film which system comprises an objective lens, means for holding the film in the back image plane of" said lens, two intersecting reflecting surfaces positioned in front of the lens to receive respectively two light beams grossing at the lens, the line of intersection being at an appreciable acute angle between 5 and 25 to the principal planes of the ,lens and two reflectors positioned respectively in the line of the, beams refiected'from said surfaces and oriented to rotate the beams oppositely through 90and to reflect them into stereoscopic coincidence at the front focus of the lens.

2. An optical system according which the two intersecting reflecting surfaces are the side facesof an isosceles prism whose apex is the line of intersection and whose base face is adjacent to'the lens, whereby the beams between the surfaces and saidtwo reflectors respectively passed through the opposite reflecting surface.

' 3. An optical system according to claim 1 in to claim 1 in 7. An optical system according to claim 5 in which .the prism is equilateral.

8. An optical system according to claim 5 in which said acute angle is about 15. I

9. A stereoscopic attachment for a camer having an objective lens comprising a housing with a front window and a second window in one of the walls which is approximately horizontal, an equilateral prism mounted in the housing with its base face adjacent to said second window, means on the housing for attaching it to the lens with the second window and the prism in alignment with the lens and with said base face at an' appreciableacute angle to the principal planes of the lens and two reflectors mounted in the housing to receive light beams through the front window, to rotate them oppositely through and-to reflect them respectively through the side 11. A- stereoscopic attachment'according to claim 9 in which said acute angleis between 5 and 25.

12.- A stereoscopic attachment according .to claim 9 in which said acute angle is'about 15.

POMPEY MAINARDI. MARCUS N. MAINARDI. 

